1. Field of the Invention
The present invention relates to an Organic Light Emitting Display (OLED) and its method of fabrication, and more particularly, the present invention relates to an OLED and its method of fabrication, capable of omitting a process of patterning a second pixel electrode by forming a first pixel electrode, forming a pixel-defining layer including an opening on the first pixel electrode, and forming the second pixel electrode and a third pixel electrode in the opening using a shadow mask as a mask.
2. Description of the Related Art
In general, an organic light emitting diode has a structure in which an organic thin layer is disposed between a first electrode (an anode) which is a transparent electrode formed of ITO and a second electrode (a cathode) formed of a metal having a low work function, such as Ca, Li, Al, and so on. When a forward voltage is supplied to the organic light emitting diode, a hole and an electron are injected into the organic layer, the hole and electron injected into the organic thin layer are re-combined with each other to generate an exciton, and the exciton transitions from an excited state to a ground state to thereby emit light.
The first electrode is formed as a reflective electrode for reflecting light, and the second is formed as a transmissive electrode for transmitting light, thereby forming an organic light emitting diode capable of emitting light emitted from the organic thin layer in a direction of the second electrode.
FIG. 1 is a cross-sectional view showing a method of fabricating an OLED.
Referring to FIG. 1, a buffer layer 110 is formed on a substrate 100, a semiconductor layer composed of source and drain regions 120a and 120b and a channel region 121 is formed on the buffer layer 110, a gate electrode 131 is formed on a gate insulating layer 130, and source and drain electrodes 150a and 150b are formed on an interlayer insulating layer and electrically connected to the source and drain regions 120a and 120b through contact holes.
An organic light emitting diode is formed on the substrate 100. The organic light emitting diode includes: a first electrode 180 acting as an anode electrically connected to the drain electrode 150b through a via-hole and formed on a passivation layer 160 and a planarization layer 170 which are formed over a thin film transistor; an organic layer 191 formed on the first electrode 180 exposed through an opening in a pixel-defining layer 190; and a second electrode 192 formed on the organic layer 191.
The first electrode 180 is formed of an Indium Tin Oxide (ITO) layer 180a, an Ag layer 180b is formed on the ITO layer 180a, and an ITO layer 180c is formed on the Ag layer 180b. Then, a photoresist pattern is formed on the ITO layer 180c, and the first electrode layer having a deposited structure of the ITO layer/Ag layer/ITO layer is etched using the photoresist pattern as a mask, thereby forming the first electrode 180 having a deposited structure of the ITO layer/Ag layer/ITO layer. Then, the photoresist pattern is removed using a stripping solution, and the substrate having the first electrode is cleaned.
In this process, the etching process may be a wet etching or dry etching process. In the case of the wet etching, an acidic solution, such as H3PO4, CH3COOH, HNO3, H2SO4, and so on, or a mixture thereof is supplied or injected onto a region to be etched to obtain a desired pattern. A strong basic solution is needed in a cleaning or stripping process after the etching.
However, since the strong acidic or basic chemicals used in the etching, cleaning and stripping processes are in direct contact with the ITO layer 180a and the Ag layer 180b used as the pixel electrode 180, a metal oxide layer is formed due to oxidation of Ag at an interface between the ITO layer 180a and the Ag layer 180b, and thus adhesion between the lower ITO layer and the Ag layer may be weakened to cause the Ag layer to be peeled-off from the lower ITO layer during the process.